Titanium oxide thin Films were deposited by D. C. reactive magnetron sputtering from a pure 99. 9% Ti disk. The results of the electrochemical impedance spectroscopy（EIS） investigation indicated that the diameters of the capacitive arcs of the TiO2 with UV and anodic bias potential were much smaller than those of dark space,thus inviting a higher photoelectrocatalytic activity. When an external bias was applied on the TiO2, the arc of EIS Nyquist plot decreased obviously than without the bias, suggesting more efficient separation of the photo - generated carriers. The degradation of azocarmine was most effective when the external potential is up to 0.3V.